Versatile, rapid and robust nano-positioning of single-photon emitters by AFM-nanoxerography.

Atomic force microscopy (AFM) nanoxerography was successfully used to direct the assembly of colloidal nanodiamonds (NDs) containing nitrogen-vacancy (NV) centres on electrostatically patterned surfaces. This study reveals that the number of deposited NDs can be controlled by tuning the surface potentials of positively charged dots on a negatively charged background written by AFM in a thin PMMA electret film, yielding assemblies down to a unique single-photon emitter with very good selectivity. The mechanisms of the ND directed assembly are attested by numerical simulations. This robust deterministic nano-positioning of quantum emitters thus offers great opportunities for ultimate applications in nanophotonics for quantum technologies.

Near-field microscopy with a scanning nitrogen-vacancy color center in a diamond nanocrystal: A brief review.

We review our recent developments of near-field scanning optical microscopy (NSOM) that uses an active tip made of a single fluorescent nanodiamond (ND) grafted onto the apex of a substrate fiber tip. The ND hosting a limited number of nitrogen-vacancy (NV) color centers, such a tip is a scanning quantum source of light. The method for preparing the ND-based tips and their basic properties are summarized. Then we discuss theoretically the concept of spatial resolution that is achievable in this special NSOM configuration and find it to be only limited by the scan height over the imaged system, in contrast with the standard aperture-tip NSOM whose resolution depends critically on both the scan height and aperture diameter. Finally, we describe a scheme we have introduced recently for high-resolution imaging of nanoplasmonic structures with ND-based tips that is capable of approaching the ultimate resolution anticipated by theory.

Sorting nanoparticles with intertwined plasmonic and thermo-hydrodynamical forces.

We exploit plasmonic and thermo-hydrodynamical forces to sort gold nanoparticles in a microfluidic environment. In the appropriate regime, the experimental data extracted from a Brownian statistical analysis of the kinetic motions are in good agreement with Mie-type theoretical evaluations of the optical forces acting on the nanoparticles in the plasmonic near field. This analysis enables us to demonstrate the importance of thermal and hydrodynamical effects in a sorting perspective.

Diffraction regimes of single holes.

We investigate both experimentally and theoretically the far-field diffraction patterns of single circular apertures as a function of their diameters d and at a given illumination wavelength λ. We observe the transition between the well-known pseudoscalar regime of large holes (d≫λ) and the less-known vectorial regime of subwavelength ones (d≪λ). Four different diffraction regimes are identified for different d/λ regions, each one with its polarization dependence. A thorough comparison with a theoretical model, which takes into account both finite hole size and the dielectric properties of the metal, allows us to explain and understand the physical processes leading to this behavior. Our results reveal the subtle interplay between two competing factors, one related to polarization symmetries associated with surface-plasmon excitations and the other originating in the coupling of the field to the waveguide mode of the aperture.

[Elderly patients in the emergency department: a selection of some recent publications]. / Gériatrie aux urgences: une sélection de publications récentes.

Geriatric patients presenting to the ED are at high risk of mortality as well as of cognitive or functional decline. Thus, ED is an ideal spot for interventions that can improve their outcome. In this article, we summarize six recent studies, regarding the utilization of prognostic evaluation scores in geriatric patients presenting to the ED, adverse drug reactions, the significance of elevated troponin in patients who have remained on the ground after a fall, the rationale of performing head CT in patients without focal neurologic findings after a fall, the ideal treatment of a proximal femoral fracture and the excessive use of urinary catheters in the ED.

Brownian motion in a designer force field: dynamical effects of negative refraction on nanoparticles.

Photonic crystals (PC) have demonstrated unique features that have renewed the fields of classical and quantum optics. Although holding great promises, associated mechanical effects have proven challenging to observe. We demonstrate for the first time that one of the most salient properties of PC, namely negative refraction, can induce specific forces on metal nanoparticles. By integrating a periodically patterned metal film in a fluidic cell, we show that near-field optical forces associated with negatively refracted surface plasmons are capable of controlling particle trajectories. Coupling particle motions to PC band structures draws new approaches and strategies for parallel and high resolution all-optical control of particle flows with applications for micro- and nanofluidic systems.

Plasmonic coherent drive of an optical trap.

We demonstrate that optical trapping can be driven by delocalized surface plasmon modes resonantly excited within a standing wave trap. Dynamical modifications are shown to be determined by the near-field symmetry of the plasmonic modes with negligible thermal effect. With low trapping powers and polarization control, remarkable stiffness enhancements are recorded, the larger the smaller the particle. The results can be simply modeled accounting for a coherent interaction between the plasmon field and the Gaussian standing wave of the trap.

Fluorescent oxide nanoparticles adapted to active tips for near-field optics.

We present a new kind of fluorescent oxide nanoparticle (NP) with properties well suited to active-tip based near-field optics. These particles with an average diameter in the 5-10 nm range are produced by low energy cluster beam deposition (LECBD) from a YAG:Ce3+ target. They are studied by transmission electron microscopy (TEM), x-ray photoelectron spectroscopy (XPS), cathodoluminescence, near-field scanning optical microscopy (NSOM) and fluorescence in the photon-counting mode. Particles of extreme photo-stability as small as 10 nm in size are observed. These emitters are validated as building blocks of active NSOM tips by coating a standard optical tip with a 10 nm thick layer of YAG:Ce3+ particles directly in the LECBD reactor and by subsequently performing NSOM imaging of test surfaces.